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Polymer semiconductors (PSCs) are a desirable class of materials for next-generation electronics. However, the conformational complexity associated with macromolecules, as well as the presence of u...

It is challenging to realize both a fully conjugated rigid polymer backbone and high molecular weight at the same time. Previously, we reported a DPP-FT4 polymer with molecular weight up to 30 kDa. A new design and synthesis was required to overcome this limitation. Here, we report the successful synthesis of a conjugated semiconducting polymer with tunable molecular weight over a wide range. Through molecular design and synthesis control, our new polymer can be selectively prepared with number-averaged molecular weight (Mn) ranging from approximately 20 to 100 kDa, realizing both high molecular weight and high solubility at the same time. Four polymers within this range were investigated, with particular emphasis on Mn of 50 kDa (P2) and 97 kDa (P4). The relationships between molecular weight and polymer properties, molecular packing, and electrical behavior are explored in detail. All the polymers in this series are fully soluble in nonchlorinated solvents at room temperature, which is promising for lar...

Semiconducting conjugated polymers possess attractive optoelectronic properties and low-cost solution processability and are inherently mechanically flexible. However, the device performance is susceptible to the fabrication methods because of the relatively weak intermolecular interaction of the polymers and their inherent conformational and energetic disorder. An efficient fabrication technique for large-scale integration of high-quality polymer architectures is essential for realizing high-performance optoelectronic devices. Here, we report an efficient method for fabrication of polymer nanowire arrays with a precise position, a smooth surface, a homogeneous size, high crystallinity, and ordered molecular packing. The controllable dewetting dynamics on a template with asymmetric wettability permits the formation of discrete capillary bridges, resulting in the ordered molecular packing arising from unidirectional recession of the three-phase contact line. The high quality of nanowire architectures is evidenced by the morphological characteristics and hybrid edge-on and face-on molecular packing with high crystallinity. On the basis of these high-quality nanowire arrays, photodetectors with a responsivity of 84.7 A W-1 and detectivity of >1012 Jones are realized. Our results provide a platform for integration of high-quality polymer architectures for use in high-performance optoelectronic devices.

High-performance fused thiophene–diketopyrrolopyrrole copolymer (PTDPPTFT4) top-contact transistors have been fabricated using a top contact metal lift-off process. The source–drain (S/D) top metal contacts were directly formed by i-line photolithographic patterning over the organic semiconductor channel through a lift-off method based on a negative tone photoresist. With a fluorinated imaging material (Orthogonal OScR 2312), devices exhibit field effect mobilities up to 2.56 cm 2 V −1 s −1 and on/off ratio >10 7 , with channel lengths precisely patterned down to 10 μm. Devices prepared from the lift-off process through a commercial negative tone photoresist such as AZ nLOF 2020 instead of the fluorinated photoresist exhibited considerable degradation. De-ionized (DI) water, aqueous tetramethyl ammonium hydroxide (TMAH) developer and organic stripper do not apparently degrade the performance of the PTDPPTFT4 transistors upon dip testing. Indeed the observed degradation originates from the incomplete development of the unexposed photoresist in the TMAH developer. This is detrimental to the PTDPPTFT4 channel due to formation of resist residue over the organic semiconductor surface. This residue eventually leads to a significant increase of the S/D contact resistance upon metal contact deposition.

High performance organic thin-film transistors (OTFTs) are fabricated on an epoxy based photo-patternable organic gate insulating layer (p-OGI) using a top contact thin-film transistor configuration. This negative tone p-OGI material is composed of an epoxy type polymer resin, a polymeric epoxy cross-linker, and a sulfonium photoacid generator (PAG). Features from p-OGI can be precisely patterned down to ∼3 μm via i-line photolithography. In order to evaluate the potential of this epoxy type resin as a gate insulator, we evaluated the dielectric properties of the p-OGI and its gate insulating performance upon fabricating solution processed OTFTs using an organic semiconductor (OSC), namely tetrathienoacene-DPP copolymer (PTDPPTFT4). Results show that the PTDPPTFT4 based OTFTs with this p-OGI exhibit field-effect mobilities up to 1 cm2 V−1 s−1, indicating the potential of high performance solution processed OTFT based on an epoxy based p-OGI/OSC system.

Using non-chlorinated solvents for polymer device fabrication is highly desirable to avoid the negative environmental and health effects of chlorinated solvents. Here, a non-chlorinated mixed solvent system, composed by a mixture of tetrahydronaphthalene and p­-xylene, is described for processing a high mobility donor-acceptor fused thiophene-diketopyrrolopyrrole copolymer (PTDPPTFT4) in thin film transistors. The effects of the use of a mixed solvent system on the device performance, e.g., charge transport, morphology, and molecular packing, are investigated. p-Xylene is chosen to promote polymer aggregation in solution, while a higher boiling point solvent, tetrahydronaphthalene, is used to allow a longer evaporation time and better solubility, which further facilitates morphological tuning. By optimizing the ratio of the two solvents, the charge transport characteristics of the polymer semiconductor device are observed to significantly improve for polymer devices deposited by spin coating and solution shearing. Average charge carrier mobilities of 3.13 cm2 V−1 s−1 and a maximum value as high as 3.94 cm2 V−1 s−1 are obtained by solution shearing. The combination of non-chlorinated mixed solvents and the solution shearing film deposition provide a practical and environmentally-friendly approach to achieve high performance polymer transistor devices.

Photolithography is applied to pattern PTDC16DPPTDC17FT4-based organic thin-film transistors (OTFTs) array on the ionexchanged NAS glass substrate with pattern features down to 10 µm. Result demonstrates high stability and excellent uniformity of bottom contact OTFT devices incorporated with a photopatternable polymer gate insulator over 2" × 2" Gorilla glass substrates.

Corning has developed three generations of polymeric organic semiconducting (OSC) materials, each with progressively improved electronic performance and processability. These materials possess excellent solubility, mobility and stability. Stanford University has developed a new polymer dielectric material based on a fluoroelastomer. Combined with Coming's OSC polymers, this enables easy to fabricate transistors with high transconductance, low driving voltage and excellent device stability, even in water.

Both high gain and transconductance at low operating voltages are essential for practical applications of organic field-effect transistors (OFETs). Here, we describe the significance of the double-layer capacitance effect in polar rubbery dielectrics, even when present in a very low ion concentration and conductivity. We observed that this effect can greatly enhance the OFET transconductance when driven at low voltages. Specifically, when the polar elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) was used as the dielectric layer, despite a thickness of several micrometers, we obtained a transconductance per channel width 30 times higher than that measured for the same organic semiconductors fabricated on a semicrystalline PVDF-HFP with a similar thickness. After a series of detailed experimental investigations, we attribute the above observation to the double-layer capacitance effect, even though the ionic conductivity is as low as 10–10 S/cm. Different from previously reported OFETs with double-layer capacitance effects, our devices showed unprecedented high bias-stress stability in air and even in water., info:eu-repo/semantics/published

Dual‐gate field‐effect transistors (FETs) based on organic semiconductor polymer and SiOx as the topmost active sensing layer permit monitoring of pH in physiologically relevant conditions in a fast and reversible fashion. Beyond that, due to the bottom gate‐induced field effect, such sensors exhibit tunable sensitivity and provide faster continuous measurements compared to conventional bulky glass bulb pH sensors. pH response of bare SiOx is evaluated independently by means of voltmeter measurements. When assembled in dual‐gate architecture, the pH response of FET devices scales in agreement with the theoretical model, which assumes capacitive coupling, exhibiting an amplification of up to 10. This opens up the possibility for reversible and reliable sensing based on organic semiconductors well beyond pH sensors., R.P. and A.M.F. contributed equally to this work. R.P. acknowledges support from the Marie Curie Cofund, Beatriu de Pinós Fellowship (AGAUR 2014 BP‐A 00094). A.M.F. acknowledges a postdoctoral fellowship support from the Natural Sciences and Engineering Research Council (NSERC) of Canada. This project was supported by the Stanford Catalyst for Collaborative Solutions Program and the Beijing Institute of Collaborative Innovation (BICI).

Deformable electronic devices that are impervious to mechanical influence when mounted on surfaces of dynamically changing soft matters have great potential for next-generation implantable bioelectronic devices. Here, deformable field-effect transistors (FETs) composed of single organic nanowires (NWs) as the semiconductor are presented. The NWs are composed of fused thiophene diketopyrrolopyrrole based polymer semiconductor and high-molecular-weight polyethylene oxide as both the molecular binder and deformability enhancer. The obtained transistors show high field-effect mobility >8 cm2 V-1 s-1 with poly(vinylidenefluoride-co-trifluoroethylene) polymer dielectric and can easily be deformed by applied strains (both 100% tensile and compressive strains). The electrical reliability and mechanical durability of the NWs can be significantly enhanced by forming serpentine-like structures of the NWs. Remarkably, the fully deformable NW FETs withstand 3D volume changes (>1700% and reverting back to original state) of a rubber balloon with constant current output, on the surface of which it is attached. The deformable transistors can robustly operate without noticeable degradation on a mechanically dynamic soft matter surface, e.g., a pulsating balloon (pulse rate: 40 min-1 (0.67 Hz) and 40% volume expansion) that mimics a beating heart, which underscores its potential for future biomedical applications.

Injection of photoexcited electrons from colloidal PbS quantum dots into TiO(2) nanoparticles is investigated. The electron affinity and ionization potential of PbS quantum dots, inferred from cyclic voltammetry measurements, show strong size dependence due to quantum confinement. On the basis of the measured energy levels, photoexcited electrons should transfer efficiently from the quantum dots into TiO(2) only for quantum-dot diameter below approximately 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of PbS quantum dots coupled to titanium dioxide nanoparticles are consistent with electron transfer for small quantum dots. The measured electron transfer time is surprisingly slow ( approximately 100 ns), and implications of this for future photovoltaics will be discussed. Initial results obtained from solar cells sensitized with PbS quantum dots are presented.

The design of polymer semiconductors possessing high charge transport performance, coupled with good ductility, remains a challenge. Understanding the distribution and behavior of both crystalline domains and amorphous regions in conjugated polymer films, upon an applied stress, shall provide general guiding principles to design stretchable organic semiconductors. Structure–property relationships (especially in both side chain and backbone engineering) are investigated for a series of poly(tetrathienoacene-diketopyrrolopyrrole) polymers. It is observed that the fused thiophene diketopyrrolopyrrole-based polymer, when incorporated with branched side chains and an additional thiophene spacer in the backbone, exhibits improved mechanical endurance and, in addition, does not show crack propagation until 40% strain. Furthermore, this polymer exhibits a hole mobility of 0.1 cm2 V−1 s−1 even at 100% strain or after recovered from strain, which reveals prominent continuity and viscoelasticity of the polymer thin film. It is also observed that the molecular packing orientations (either edge-on or face-on) significantly affect the mechanical compliance of the polymer films. The improved stretchability of the polymers is attributed to both the presence of soft amorphous regions and the intrinsic packing arrangement of its crystalline domains.

Recently much interest has been directed toward solution processable polymeric semi-conductor materials containing thiophene based moieties.[1] In particular, dialkylated tetrathienoacene (fused thiophene) copolymers have been used as high mobility semiconductors in field-effect transistors with a field-effect hole mobility exceeding 0.3 cm2/Vs.[2] Expansion of this class of materials to include new materials with either linear (DCnFT4) or branched (DbCnFT4) di-alkyl-substituted fused thiophenes has been achieved with the development of two distinct synthetic routes for ring formation and the introduction of the side-chains.DC17FT4 was prepared from tetrabromothieno[3,2-b]thiophene through a sequence of diketone formation, cyclization, hydrolysis and decarboxylation. Synthesis of the new compound di-2,4,4-trimethylpentyl-FT4 (DbC8FT4) has been accomplished in a more complex 8 step process, featuring a mono-ketone-ester as a key intermediate.DCnFT4 can be brominated in the 2- and 6-positions with NBS. The dibromide can then be used to form copolymers through cross coupling reactions. These polymers are solution processable semi-conductors. The polymers have been characterized by GPC and within organic thin-film transistor (OTFT) devices.

The aerosol chemical vapor deposition (ACVD) process allows for the synthesis of nanostructured films with well tuned morphologies that can be controlled based on the desired functionality and application. A robust understanding of the process parameters that result in desired features of the film is elucidated. One dimensional TiO2 nanostructured columns that have superior properties for solar energy harvesting and conversion applications were deposited on tin doped indium oxide (ITO) substrates. The sintering of the deposited particles was a key factor in the growth of the 1D structure with desired crystal planes. By ensuring that the sintering rate is faster than the arrival rate of deposited particles; a 1D columnar structure could be obtained. The sintering rate was controlled by the temperature and depositing particle size. As the columns grew in length, the increased thermal conduction resistance resulted in a drop in temperature and subsequently a slowing of the sintering process in upper regions of the film. This led to growth of branched structures rather than continued growth in a preferred direction. The growth of the branched structure could be overcome by enhancing the sintering rate by increasing the substrate temperature or reducing the depositing particle size (by lowering the feed rate of the precursor). The phenomenon was also confirmed by using different deposition substrates, such as FTO and glass. Dye sensitized solar cell performance efficiencies with different column lengths of 2 and 7 µm were determined to be 1.8 and 2.7% respectively.